Model Relation classes are for defining relationships between models, and facilitating JOINs between them during querying. They require knowing at least the model names of the two models they join, and require each to have proper Private and Foreign key fields setup. (HABTM are different) Once those two models are setup correctly, and the relation object has the names of each, it can magically figure out what tables must be joined on what fields during querying.
Methods inherited from EE_Has_Many_Relation
Methods inherited from EE_Model_Relation_Base